My circuit has both 8K SRAM and 8K EEPROM. In my thinking as part of a sub function for example say the mcu was being used in a robot? the main program is running. now the robot wants to use its sensors well it calls to the program on the PC and says download sensor routine. but first save current sub routine in EEPROM. and then execute in ram the downloaded sub. complete the routine and then copy the previouse one back from the eeprom and continue. This is my thinking.